Current research encompasses projects which are more fundamental in nature (‘discovery driven’) – such as studies aimed at systematically uncovering the chemistry of new types of chemical bond, as well as those which are targeted at specific applications - such as sensors for toxic environmental contaminants and catalysts for hydrogen production from B/N containing materials. An over-arching theme of much of the work is the stabilization and application of compounds with potent Lewis acidity.

Three main areas encompass a significant proportion of recent research efforts:

The coordination chemistry of CO at low-valent transition metals remains one of the cornerstones of organometallic chemistry, and that of the dinitrogen molecule underpins synthetic attempts to mimic biological activation of N2. By contrast coordination of the isoelectronic 10 valence electron molecule BF has not previously been achieved. Recent studies in the Aldridge group have addressed this deficiency, allowing for the first time the structural characterization of a transition metal complex of BF (Angew. Chem., Int. Ed. 2009, 48, 3669; highlight: Angew. Chem., Int. Ed.2010, 49, 3412). Moreover, a terminal mode of coordination can be accessed by the use of the heavier group 13 monohalide fragment GaI (J. Am. Chem. Soc.2008, 130, 5449; J. Am. Chem. Soc.2008, 130, 16111; also subject of a highlight article in Angew. Chem., Int. Ed.2008, 47, 6326). These synthetic and structural studies have been complemented by in-depth analyses of electronic structure revealing, for example, weaker pi bonding and readier heterolytic cleavage for the BF diatomic molecule over CO (our work in this area was recently reviewed in a feature article: Chem. Commun.2009, 1157).

These studies form part of a broader programme aimed at developing versatile synthetic routes to complexes containing unsaturated group 13 ligand systems (e.g. metal boron double bonds), evaluating their electronic structure, and exploiting their fundamental patterns of reactivity – ultimately towards the catalytic functionalization of organic substrates. These studies have led to the landmark results such as the first Fe=B double bond (J. Am. Chem. Soc.2003, 125, 6356), the first examples of metathesis chemistry involving M=B bonds (Angew. Chem., Int. Ed.2005, 44, 7457; highlighted in Science2005310, 747); and to the functionalization of organic substrates by borylene transfer and/or cycloaddition (Angew. Chem., Int. Ed.2006, 45, 3513; Angew. Chem., Int. Ed. 2006, 45, 6118). Aspects of this fundamental chemistry have been included in recent editions of undergraduate chemistry textbooks.

Recent work sponsored by the EPSRC has examined synthetic and stabilization strategies for cationic 14-electron group 9 metal complexes stabilized by strongly electron donating N-heterocyclic carbene ligands. One of the prime motivating forces for our work in this area is to examine the possibility for using such systems in catalytic processes, and in particular for the trapping and characterization of potential intermediates in CC and BN dehydrogenation chemistry. With this in mind the trapped metathesis intermediate [(IMes)2M(H)2Cl(Na)]+[BArf4]-, for example, serves as a convenient source of [(IMes)2M(H)2]+ (by loss of NaCl) and has been exploited in the synthesis of the first examples of transition metal aminoborane complexes (Angew. Chem., Int. Ed. 2010, 49, 921; J. Am. Chem. Soc. 2010, 132, 10578). Systems of this sort are of interest as model intermediates in the metal-catalysed dehydrogenation of amineboranes and provide an interesting contrast – in coordination chemistry terms – with isoelectronic alkene donors (‘end-on’ vs. ‘side-on’). Ongoing work has revealed the formation (and structural characterization) of 14-electron primary boryl hydride species under catalytic conditions and is examining approaches to the key technological problem of B/N fuel rehydrogenation using high energy sources of the H2 fragment.

ANION AND NEUTRAL MOLECULE SENSORS:

The binding of anions by receptor molecules is an area of enormous recent research interest, which is not only relevant to biological systems, but has widespread applications, for example in catalysis and sensor systems. From the viewpoint of sensor design, key features are selectivity (i.e. the recognition of the target anion over possible contaminants) and signalling (i.e. the triggering of a measurable response on anion binding). A wide variety of chemical strategies have been employed to selectively bind anions, and we have been using group 13 based Lewis acids in this area – with the selectivity for given anions based, for example, on the strength of the donor/acceptor bond formed (e.g. for fluoride, F-) or on the complementary geometry of the binding sites and target anion (e.g. for CN-or [CH3CO2]-)

More applied work has targeted the use of redox-active Lewis acids in the development of highly sensitive, highly selective sensors for F-/HF and CN-/HCN. This facet of the group’s research efforts has led to the realization of new synthetic methodologies for ferrocene-derivatized Lewis acids and ultimately to the development of a simple colorimetric swab technology which allows for the detection of chemical warfare agents (CWAs) in both the (weaponized) liquid and vapour phases. This work has been funded by back-to-back EPSRC grants and the resulting patented IP is the basis for current commercialization negotiations. Despite the commercial sensitivities, some aspects of this work have recently been published: Angew. Chem., Int. Ed.2005, 44, 3606; Dalton Trans.2007, 3486; Inorg. Chem.2008, 47, 793; Chem. Eur. J.2008, 14, 7525; Inorg. Chem.2010, 49, 157.

A key future target in this area, ultimately aimed at improving device sensitivity, is the development of catalytic sensors. The aim is to identify host/guest complexes formed between receptor and target analyte which will catalyze an orthogonal reaction. Our approach utilizes electron transfer chemistry as the basis for catalysis, e.g. of a dye bleaching reaction.